1. Field of the Invention
The present invention relates to a tripod type constant velocity universal joint used in a power transmitting section of automobiles, aircraft, ships, and industrial machinery.
2. Description of the Related Art
For example, among constant velocity universal joints used as means for transmitting a rotational power of an automobile engine to its wheels at a constant speed is a tripod type constant velocity joint. This tripod type constant velocity universal joint connects a driving side shaft and a driven side shaft together and can transmit a rotational torque between them at a constant velocity even if there is an operating angle between them. The tripod type constant velocity universal joint even permits a relative displacement in an axial direction.
FIG. 15 and FIG. 16 show a fundamental structure of a tripod type constant velocity universal joint. This constant velocity universal joint is composed of, as essential structural members, a tripod member 2 with three radially projecting leg shafts 1, an outer joint member 5 with three axially extending track grooves 3 formed on the inner circumferential surface of the outer joint member, and rollers 7. Each of the track grooves 3 has at both sides axially extending roller guide surfaces 4. The rollers 7 are mounted on the leg shafts 1 of the tripod member 2 through a plurality of needle rollers 6 and positioned in the track grooves 3 of the outer joint member. The rollers 7 are guided on their external circumferential surfaces by the roller guide surfaces 4 provided at the both sides of the track grooves.
The tripod member 2 is fitted over a serration part (or spline part) formed on an end part of the other shaft, not shown, and is secured. As shown in FIG. 17, a plurality of the needle rollers 6 are arranged, so that they can rotate, on an outer circumferential surface of the leg shaft 1 of the tripod member 2. The needle rollers 6 are limited with respect to their displacement on the leg shaft 1 in the axial direction by washers 8 and 9 installed at the base and top parts of the leg shaft 1, and a retaining ring 10 secured at the top part of the leg shaft 1. The outer circumferential surface of the leg shaft 1 of the tripod member 2 has a cylindrical shape, and rollers 7 are fitted over the outer circumferential surface of the leg shaft 1 through the needle rollers 6 so that they can rotate. The inner circumferential surface of the roller 7 has a cylindrical shape and the outer surface thereof has a genuine partial sphere shape.
The outer joint member 5 forms a cylindrical cup with one end open and the other end closed, with the other shaft, not shown, being integrally provided at the other end of the outer joint member. Three axial track grooves 3 are formed on the circumference around a center shaft at intervals of 120 degrees on the inner circumferential surface of the outer joint member 5. At both sides of each track groove 3 are the two roller guide surfaces 4, and, as shown in FIG. 18, the roller guide surface 4 makes angular contact with the roller 7 at two points A and B. This is done by forming the roller guide surface 4 in the shape of a gothic arch.
In this tripod type constant velocity universal joint, power is transmitted by the connection between the roller guide surfaces 4 of the outer joint member 5 and the rollers 7 of the tripod member 2. The rollers 7 absorb plunging by rotating along the roller guide surfaces 4. In the case of power transmission when the axis of the outer joint member 5 and the axis of the tripod member 2 are aligned, or an operating angle is 0 degree, the point of intersection of the axes of each leg shaft 1 is located on the axis of the outer joint member 5. In this way the rollers 7 rotate while maintaining dual contact points with the roller guide surfaces 4. When there is an operating angle, although the magnitude of the contact force fluctuates depending on the rotational phase, the operation of the tripod type constant velocity universal joint is stable because the rollers and the roller guide surfaces 4 are always in contact with each other at the two points A and B.
The tripod type constant velocity universal joint described above is a sliding type in which relative displacement, caused by plunging, between the two shafts in the axial direction is allowed. Torque is transmitted by connecting the tripod member 2 with one shaft, connecting the outer joint member 5 with the other shaft, and positioning the leg shafts 1 of the tripod member 2 in the track grooves 3 of the outer joint member 5. In this construction, the tripod member 2 is provided with the three leg shafts 1 projecting in an axial direction, and the outer joint member 5 is provided with the three track grooves 3 extending in the axial direction.
In this tripod type constant velocity universal joint, because the roller 7 and the roller guide surface 4 are in angular contact at the points A and B, and the roller 7 does not contact with the center part and both sides of the roller guide surface 4, a strong edge load is not created, the needle rollers 6 do not become skew, and friction resistance does not increase. Furthermore, because of lower eccentric load, rotational moment caused in the roller 7 acting at a right angle to the leg shaft 1 around the axis thereof can be decreased, and frictional force and induced thrust that cause vibration can be reduced. Also, movement in the axial direction when transmitting rotational torque with an operating angle becomes smooth, so that induced thrust is reduced.
However, conventional tripod type constant velocity universal joints are usually mounted on vehicles operating at low angles, for example equal to or less than 4 degrees, and for vehicles operating at high angles, for example equal to or more than 7 degrees, tripod type constant velocity universal joints of a double roller type are used taking into consideration a higher level of vibration in such applications. The conventional tripod type constant velocity universal joints described above correspond to a single roller type.
A tripod type constant velocity universal joint of a double roller type is provided with a roller assembly each contained as a unit. The roller assembly is composed of a circular inner roller which is fitted over the outer circumferential surface of a leg shaft, and an outer roller positioned within the track groove which rotates in the axial direction of an outer joint member. Needle rollers are interposed between the inner and outer rollers. Within the roller assembly the inner and outer rollers are individually rotatable.
In this tripod type constant velocity universal joint, the roller assembly composed of the inner and outer rollers can swing freely with respect to the leg shaft. Therefore, when transmitting a rotational force at a high operating angle between the outer joint member and the tripod member, the roller assembly can rotate only in the axial direction of the outer joint member, and the vibration inducing force of the outer joint member can be absorbed by the rotation of the needle rollers, so that sliding resistance can be reduced. Furthermore, the moment acting to incline the roller assembly during operation becomes smaller, the roller assembly can maintain its posture, resistance between the outer joint member and the roller assembly during rotation becomes smaller, and induced thrust can be reduced.
However, because a tripod type constant velocity universal joint of a double roller type has a structure provided with the roller assemblies composed of inner and outer rollers, using a tripod type constant velocity universal joint of this type in a vehicle which operates at a low angle causes the cost to increase.